Understanding Carcase EBVs

Selection for increased carcase yield and carcase value has become an increasingly important objective for breeders of cattle. So how do cattle producers evaluate and identify animals for use within their breeding program that have desirable genetics for the important carcase attributes? Visual appraisal is challenging as it is difficult to “see” many of the carcase traits and selection on raw scans alone is limited as no account is made for non-genetic factors such as age and nutrition. Thankfully, there are a range of BREEDPLAN Carcase EBVs available which provide producers with a useful tool when trying to answer this question.

INTERPRETING CARCASE EBVs

BREEDPLAN currently produces six Carcase EBVs in the Charolais Analysis; these are Carcase Weight, Rib Fat Depth, Rump Fat Depth, Eye Muscle Area, Intramuscular Fat (Marbling), Retail Beef Yield.

(i) CARCASE WEIGHT

Carcase Weight EBVs are estimates of the genetic differences between animals in hot standard carcase weight (as defined by AUSMEAT) at 650 days of age. Carcase Weight EBVs are expressed in kilograms (kg). Larger, more positive, Carcase Weight EBVs are generally more favourable. For example, an animal with a Carcase Weight EBV of +40 kg would be expected to produce progeny with heavier carcases at 650 days of age than an animal with a Carcase Weight EBV of +30 kg. Carcase Weight should not be confused with yield. The Carcase Weight EBV is an indication of the animal’s carcase weight and not an indication of the animal’s yield percentage.

ii) EYE MUSCLE AREA (EMA)

Eye Muscle Area (EMA) EBVs are estimates of the genetic differences between animals in eye muscle area at 12/13th rib site in a standard weight steer carcase. EMA EBVs are expressed in square centimetres (cm2).Larger, more positive, EMA EBVs are generally more favourable. For example, a bull with an EMA EBV of +4 cm2 would be expected to produce steer progeny with a larger eye muscle area than a bull with an EMA EBV of +1 cm2, relative to carcase weight

iii) RIB FAT

Rib Fat EBVs are estimates of the genetic differences between animals in fat depth at the 12/13th rib site in a standard weight steer carcase. Rib Fat EBVs are expressed in millimetres (mm). More positive or more negative Rib Fat EBVs may be more favourable, depending on your breeding goals relating to the finishing ability of your animals. A bull with a Rib Fat EBV of -0.4 mm would be expected to produce leaner calves than a bull with a Rib Fat EBV of +0.4 mm, relative to carcase weight.

(iv) RUMP FAT

Rump Fat EBVs are estimates of the genetic differences between animals in fat depth at the P8 rump site in a standard weight steer carcase. Rump Fat EBVs are expressed in millimetres (mm). More positive or more negative Rump Fat EBVs may be more favourable, depending on your breeding goals relating to the finishing ability of your animals. A bull with a Rump Fat EBV of -0.6 mm would be expected to produce leaner calves than a bull with a Rump Fat EBV of +0.6 mm, relative to carcase weight. Stock with positive Fat EBVs are likely to produce progeny that are fatter, or earlier maturing, on average than stock with lower or negative Fat EBVs. Increasing fat depth leads to a decrease in retail beef yield, but most market specifications require a minimum fat depth. Breeders aiming to breed leaner, higher yielding cattle may select for lower Fat EBVs. Breeders wishing to finish their animals earlier may tend to select animals with moderate Fat EBVs. Caution should be placed on selecting for extremely low Fat EBVs for replacement females as this may produce females that are more difficult to get in calf. Differences between Rib Fat EBVs and Rump Fat EBVs can indicate differences in fat distribution among animals..

(v) RETAIL BEEF YIELD (RBY)

Retail Beef Yield (RBY) EBVs are estimates of genetic differences between animals in boned out retail beef yield in a standard weight steer carcase. RBY EBVs are reported as differences in percentage (%) yield. Larger, more positive, RBY EBVs are generally more favourable. For example, an animal with a RBY EBV of +0.9% would be expected to produce progeny that would yield higher percentages of saleable beef in a standard weight steer carcase than an animal with a RBY EBV of +0.1%.

(vi) INTRAMUSCULAR FAT (IMF)

Intramuscular Fat (IMF) EBVs are estimates of genetic differences between animals in intramuscular fat (marbling) at the 12/13 rib site in a standard weight steer carcase. IMF EBVs are reported as differences in percentage (%) IMF. Larger, more positive, IMF EBVs are generally more favourable. For example, an animal with an IMF EBV of +0.8% would be expected to produce progeny that would express more marbling in a standard weight steer carcase than an animal with an IMF EBV of +0.1%. For markets where marbling is important (e.g. Meat Standards Australia (MSA), Japanese B2/B3 market, restaurant trade), higher IMF EBVs can increase carcase value.

Collecting Ultrasound Scan Records

For producers who wish to collect ultrasound scanning records on young animals in their herds, it is important to observe the following when collecting scan information:

Use a BREEDPLAN accredited scanner BREEDPLAN can only analyse scanning data that has been measured by a BREEDPLAN accredited scanner. A list of BREEDPLAN accredited scanners for Australia and New Zealand is available on the BREEDPLAN website.

Only scan animals when they are between 300 and 800 days of age. BREEDPLAN can analyse the scanning performance from animals that are between 300 to 800 days of age when measured.

Ensure animals are in sufficient condition to scan. Aim to scan your animals when they are in the best condition possible. As a rough guide, animals should have an average minimum rump fat depth of 5mm and an average minimum rib fat depth of 3mm. The IMF results are further optimised if the majority of animals have between 2% and 8% IMF at the time of scanning.

Only submit one set of ultrasound scanning records per animal to BREEDPLAN. BREEDPLAN will only analyse one EMA, one rib fat, one rump fat & one IMF ultrasound scanning measurement on each animal

The two graphs below show the genetic improvement gained in the Charolais breed for carcase traits. The breed has made good progress in these important traits that contribute to carcase quality. With increased selection pressure further improvement is available to breeders. Using carcase scanning and the BREEDPLAN analysis, breeders can make great gains in these traits which are not easily detected by the eye such as IMF%.

To further discuss Carcase EBVs contact staff at Southern Beef Technology Services (SBTS) Telephone 02 6773 3357 or email catriona@sbts.une.edu.au